AKAI CTV29TA weird standby

[sausagejohnson]

Hi Guys, trying to look into a problem with my Akai CTV29TA TV when pressing the remote standby button.

If the TV has been on for a few minutes and it is well warmed, then if I put it into standby, I get this 'box' effect, then the display goes down to a single raster line that very slowly shrinks inwards.

Takes around 30 seconds to fully go into standby mode.

The operation for the rest of the TV, including viewing is perfect.

I am guessing the trouble is perhaps around the flyback unit, or surrounding caps.

I have reflow soldered every large to medium solder point (including everything around the flyback).

Included are some photos of good operation, the effect when going to standby, plus some shots to show the power area:


Running Uridium on the C64. All fine.


When first going into standby mode:





20 seconds later...


10 more seconds later...




Shots near the power and flyback:




I'd be grateful if anyone could recommend an approach to fix, or let me know the terminology for the effects that I'm seeing so I can research solutions.

[llonen]

Re: AKAI CTV29TA weird standby

I take it you don't get the same effect when switching the set off at the panel switch

[R_J]

Re: AKAI CTV29TA weird standby

It looks like the drive circuit is not being turned off, Its still supplying drive signals to the horz. vert. output circuits while the b+ to the outputs has been turned off and slowly bleads down.
Its posible the relay (if used) contacts are stuck closed, I've seen similar effects when that happens.
Try giving the relay a couple taps and see if that changes what happens

Got the service manual or schematic?

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Hi llonen, when pressing the switch at the front of the TV, it is an instant off. So it doesn't have the same odd effect.

Hi R_J, thanks for that. I'll try giving it a tap or two. I'll look around for a schematic.

[Andrew F. Ali]

Re: AKAI CTV29TA weird standby

Looks to me like the large filter cap is the issue. I would also check/replace any hi-volt cap I see in the main power supply.

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Thanks Andrew, perhaps I'll look to swapping the caps in the power supply area.

I also gave the three relays a taps with the edge of a bit of off-cut wood. Didn't want to hit them too hard. But it made no difference. But perhaps it might be worth swapping the relays as well?

Been all over the net to try and get a schematic or service manual but nothing so far.

[petehall347]

Re: AKAI CTV29TA weird standby

look for a bleed down resistor that might have gone high .
not saying there is one ..just guessing .. concentrate on and around standby circuit ...

[R_J]

Re: AKAI CTV29TA weird standby

Are you saying there are two switches on this tv, one main and one standby?
when you operate the standby switch (the one where the problem occures) Can you here a relay click? If you can I would check it's contacts, the could be stuck closed
When you push the standby button to turn off the tv the main micro turns off video and signal processing, there is usually an output from the micro to turn off the main power supply, this is usually done with a relay, if the relay does'nt open the main power supply keeps running but since there is no video signal or drive signals the raster stays on untill the b+ drains off.

Check the Chassis for a number, I suspect this was made by another company

I found this schematic, It does'nt use the relay to turn off the power supply but it uses an opto coupler. But I think its different then yours

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Hi R_J, sorry I meant there is only one switch at the front.

Pressing that is instant on or off. The only way to come in and out of standby mode is with the remote. If the TV is off, the remote cannot control the TV.

I am impressed you found that schematic! Do you mind if I ask if you found that publicly or is it via a repair subscription? (oh it might be different ok)

This might confirm what you said: When going to standby, I don't hear any relay. The closest thing to a relay sound is only when powering on or coming out of standby, there are the two usual CRT "clunks".

Couldn't find any other chassis number or anything on the main board. The tube was made by LG Philips. But it probably matters little if you have the schematic.

This might also help, during this phase:



... there is a whining noise, but the TV becomes silent by this stage:

[R_J]

Re: AKAI CTV29TA weird standby

I found that schematic at eserviceinfo, its for a CT-C29nnes
That whining I suspect is just the horzontal circuit. as the voltage is dropping the frequency is also dropping and thats what you here.
So that switch on the front is a mains on/off switch (I suspect) so the remote just puts the tv into standby by turning off the main power supply, leaving the standby power supply running.
so for some reason the main power supply is not turning off like it should. If it does'nt use a relay to do it then it must be similar to this schematic where it uses a transistor to turn an opto coupler on and off which turns the primary (in this schematic) ic on and off
Without the correct schematic I'm only guessing

[llonen]

Re: AKAI CTV29TA weird standby

I would go with R_J's theory it looks like one or more of the supply rails is not being shut down in a timely manner when the set goes into standby. Check the switched side of the each relay they should be open when the set is off. Looking at the pics, I suspect the heater and drive supplies are not being de-energised

[R_J]

Re: AKAI CTV29TA weird standby

I also found this schematic
Check and post some of the ic numbers from the power supply circuit and maybe the micro and video proc. ic's

Also look on the pc board for any chassis numbers, labels sometimes they are on the side of a heat sync or the tuner

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Hi R_J, will do thanks. I'll get some numbers and compare.

@llonen. Due to the danger of working with this set while live, I'll probably just replace all suspect components, rather than test.

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Intersting, I could not locate any ICs in the power area.

But other ICs on the main board are:

* Panasonic NN5198K 243P3101
* Toshiba TA8859CP 222KB11
* Samsung N322 S3P8849XZZ-AQB9
* Philips HEF4052BP AE073 PE Un03226
* AN5891K 2D9
* ST CHN L 24C04 6 K3K331

I'll get some clean shots of the power area.

[R_J]

Re: AKAI CTV29TA weird standby

The power supply ic is mounted to the heatsink by the large capacitor

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Oh right yes. OOps



Also a couple of shots of the power area for reference:





And the mainboard numbers:



Though I realise the CTI-600V is more about the board wafers. Not sure if any other number is the board model.

[ducky29]

Re: AKAI CTV29TA weird standby

The problem is the vertical deflection ic

[sausagejohnson]

Re: AKAI CTV29TA weird standby

Thanks, R_J and ducky29. Looks you guys nailed it.

It was the power supply / vertical deflection ic.

It led me to this link:
http://www.riddledtv.com/journal/Vertical/

Now, I had already reflowed the solder on these pins before, so this time I removed most of the solder with a braid and added new solder.

Fired up the TV and let it run for a while before going into standby.

Couldn't believe my eyes that it went to standby cleanly.

The only thing... we're running around 10 degrees cooler today. So I'll keep an eye on it as the summer heat returns, but I think it's pretty well over.

R_J, thanks for all your help and time looking up the various bits and pieces and advice. Very much appreciated.

Thanks also to those who chimed in: llonen, petehall347, Andrew F. Ali. This has been an excellent learning experience.

Hooking this TV up as my large 15khz Commodore 64 display.

[petehall347]

Re: AKAI CTV29TA weird standby

glad you got it working properly ..
its been a long time since i touched a crt tv .. i never once seen that issue but they never had standby circuits .it was on or off at the button ... and the everlasting dot in the middle of the screen .

[R_J]

Re: AKAI CTV29TA weird standby

Glad you got it fixed, It looks like the chassis # is 5800-A5N110-02, one of these might be a closer schematic, for next time.